Trucks generally have rear wheel drive, and when truck beds are empty, the weight over the rear wheels may be insufficient to provide adequate traction for the rear wheel. Other vehicles such as covered cargo vans and mini-vans also encounter the same traction problem when operated with little or no load over the rear wheels. A number of innovations have been developed relating to providing extra weight or ballast for truck beds and cargo vans, and the following U.S. patents are representative of some of those innovations.
In U.S. Pat. No. 3,727,971 Sisler discloses a receptacle unit formed to fit over the upwardly arched fender section of the box of a truck bed. The unit is filled with particulate material to provide additional traction for the truck. Additional containers are attached to the unit for storage or other purposes.
Tanner, in U.S. Pat. No. 4,339,142, describes a flexible rubber tubing filled with sand for providing ballast in a motor vehicle. In U.S. Pat. No. 5,582,441 Frost discloses a hollow front bumper for vehicles that is designed to deliver sand ahead of the vehicle using a pneumatic nozzle system to assist in breaking on slippery surfaces.
Raynor, in U.S. Pat. No. 4,796,914, Chamberlain, in U.S. Pat. No. 5,172,953, Semple et al., in U.S. Pat. No. 5,080,418, and Anderson, in U.S. Pat. No. 5,330,227, all describe a ballast chamber located on the truck bed floor which can be filled with liquid or particulate solids to provide additional weight over the truck rear wheels.
An interlocking compartmentalized weight ballast for vehicles is described by Cook in U.S. Pat. No. 4,971,356, and by Grover in U.S. Pat. No. 4,902,038. Tackett, in U.S. Pat. No. 5,657,916, discloses a molded shell with hinged cover for carrying ballast in a pickup truck, the shell fitting around the wheel wells and having half the height of the truck box sidewalls. In U.S. Pat. No. 5,494,315 Heltenburg describes containers for particulate ballast which can be located along the truck bed sides and over the wheel wells of a pickup truck.
Thus, the desirable features for a traction enhancing weight or ballast system for use in the cargo compartment of a vehicle include: 1) weight occupies minimal space in the vehicle cargo bed; 2) weight should be flat to allow items to be placed atop it; 3) weight should be easy to install and remove; 4) weight should remain stationary during vehicle movement; 5) amount of weight should be easily changed; and 6) weight should resist attack by the elements. Consequently, there is an unmet need for a traction enhancing weight or ballast system with these features.